All publications and patent applications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed inventions, or that any publication specifically or implicitly referenced is prior art.
Alfalfa (Medicago sativa L.) is an important forage species for hay and pasture which has been referred to as the “Queen of the Forages” because of its high yields and feeding value. Alfalfa is recognized as the most widely adapted agronomic crop, as an effective source of biological nitrogen (N2) fixation, useful in the improvement of soil tilth, as an important source of protein yield/ha, and as an attractive source of nectar for honey bees. For a comprehensive review of the benefits of alfalfa as an agronomic crop, see Barnes et al., Highlights in the USA and Canada 1:2-24, In Alfalfa and Alfalfa Improvement, Hanson et al. (ed.), American Society of Agronomy, Monograph No. 29 (1988).
Although alfalfa originated in southwestern Asia, it is well adapted to a wide range of climates and soils in the United States. Alfalfa is classified into fall dormancy groups, numbered 1 to 10 that can be fitted into the plant hardiness zone map. Dormancy group 1 is very dormant and suited for cold climates (such varieties stop growing and go dormant over winter), and dormancy group 10 is very non-dormant and suited for very hot climates (such varieties have high growth rates over a very long growing season and would have relatively high winter activity). For a comprehensive review of geographic adaptation of alfalfa, see Melton et al., Geographic Adaptation and Cultivar Selection 20: 595-620, In Alfalfa and Alfalfa Improvement, supra. For a comprehensive review of the distribution, history and origin of alfalfa, see Michaud et al., World Distribution and Historical Development 2:25-91, In Alfalfa and Alfalfa Improvement, supra; and, Quiros et al., The Genus Medicago and the Origin of the Medicago sativa Complex 3:93-124, In Alfalfa and Alfalfa Improvement, supra.
The genus Medicago is widely distributed and comprises an array of diverse species that are either annual or perennial. The most recent taxonomic studies of the perennial species concluded that M. sativa is polymorphic. Lesins and Gillies (Taxonomy and cytogenetics of Medicago 353-386, In Alfalfa science and technology, C. H. Hanson (ed.), American Society of Agronomy, (1972)) defined the complex as M. sativa-falcata-glutinosa, and Gunn et al. (USDA Tech. Bull. No. 1574 (1978)) designated it as the M. sativa sensu lato complex.
M. sativa plants are autopolyploid organisms, or more specifically, autotetraploids. More specifically, M. sativa plants are polysomic polyploid organisms that display tetrasomic inheritance patterns.
Essentially all annual species are cleistogamous and are exclusively self-pollinated. Generally, the perennial species require tripping, as by insect visits to the floral structures, and will set seed from either self or cross-pollination. Crosses can be made among subspecies in the M. sativa complexes and between the cultivated tetraploids and wild diploids without special preparation of the parents. For a comprehensive review of the floral characteristics, plant culture, and methods of self-pollinating or hybridizing alfalfa, see D. K. Barnes, Alfalfa 9:177-187, In Hybridization of Crop Plants, Fehr et al. (ed.), American Society of Agronomy Inc. (1980).
Commercial alfalfa seed may be provided either in a synthetic variety or a hybrid variety. Commercial production of synthetic varieties may include a breeder seed production stage, a foundation seed production stage, a registered seed production stage and a certified seed production stage. Hybrid variety seed production may involve up to three stages including a breeder seed production stage, a foundation seed production stage and a certified seed production stage.
Efforts in developing healthy and productive alfalfa varieties often focus on breeding for disease and stress-resistant cultivars, for example, breeding for persistence, breeding for adaptation to specific environments, breeding for yield per se, and breeding for quality. Between 1900 and 1975 more than 160 cultivars were developed for production in North America. Most of the newer cultivars were selected for improved adaptation and multiple pest resistance. Success has been attained in breeding for resistance to fungal, bacterial, insect, and nematode pests, including, but not limited to the development of varieties tolerant/resistant to bacterial wilt and common leaf spot (see, e.g., Elgin, Jr., et al., Breeding for Disease and Nematode Resistance 827-858, In Alfalfa and Alfalfa Improvement, supra) and to the spotted alfalfa aphid and alfalfa weevil (see, e.g., Sorensen et al., Breeding for Insect Resistance 859-902, In Alfalfa and Alfalfa Improvement, supra). Breeders have had less success in breeding for yield and quality per se (see, e.g., Hill et al., Breeding for Yield and Quality 26:809-825, In Alfalfa and Alfalfa Improvement, supra), although methods have been developed that help increase productivity and yield (U.S. Pat. No. 4,045,912). Historically, yield and productivity, quality and persistence are objectives of high concern to farmers.
Many factors affect the yield, productivity and quality of alfalfa harvests. One of the many factors affecting the quality of an alfalfa harvest is the stage of development or physiological maturity of the plant at harvest time (Kalu et al., Crop Science, Vol. 23, 1167-1172, December 1983). This dependency on stage of development suggests that herbage quality can be predicted by the maturity stage of the alfalfa. And in fact, methods of classifying the morphological stage of alfalfa have been developed to assist in the prediction of herbage quality (Kalu et al., Crop Science, Vol. 21, 267-271 (March-April 1981)).
Another factor that affects yield and quality is plant lodging that can result in plant stubble being left in the field at harvest time. Lodged or downed alfalfa causes great losses to farmers because it increases mowing time and results in reductions of both the yield and the quality of the harvested crop. University research has shown that an unharvested 7-inch stubble versus a clean cut 2-inch stubble can reduce forage yield by up to one third. Thus, alfalfa plants with improved standability are desirable because they require less mowing time and have a higher forage yield with improved forage quality.
Recovery time between harvests also limits overall alfalfa yields. A faster recovery between harvest shortens the number of days between harvests, which therefore maximizes the number of harvests and net yield for each season. Growers recognize and value the importance of this characteristic for its contribution to the season's net yield per acre. Additionally, fast recovery also contributes to moisture conservation, weed control and forage quality.
The “French” types of alfalfa include Flemish (or Flamande), Poitou, and Provence. North American alfalfa breeders have generally grouped the French alfalfa lines, including the French varieties ‘Europe’ (or ‘Europa’) and ‘Mercedes’, into the Flemish type. Flemish-type alfalfa varieties are characterized as being fast to recover after cutting, early to mature, vigorous, generally resistant to foliar diseases, susceptible to root and crown diseases, and moderately winter hardy. However, the Flemish-type alfalfa varieties are not considered to be adapted to North American growing conditions (see, e.g., Barnes et al., Alfalfa germplasm in the United States: Genetic vulnerability, use, improvement, and maintenance. USDA Tech. Bull. 1571, 21 pages (1977); Miller, D. and B. Melton, Description of Alfalfa Germplasm Culitvars and Germplasm Sources. New Mexico Agric. Exp. Stn. Special Report 53, 497 pages (1983)). Thus, while the French alfalfa varieties have some characteristics that would be beneficial for alfalfa production in the United States and Canada, they are not directly useful as North American alfalfa varieties due to their non-adaptability to its production and growing conditions.
As demonstrated by this review, there is a real need for alfalfa varieties with improved standability and/or faster recovery after spring green-up or faster recovery after harvest. The present invention provides alfalfa plants with improved standability and faster recovery after spring green-up or after harvest and methods of selection, breeding and production that use such plants. The alfalfa plants provided by this invention will reduce field losses from downed alfalfa, and provide for a better season long-distribution of yield, faster ground cover after spring green-up or after harvest, flexible harvest window, more net yield each season, equipment and labor efficiencies and management flexibility.